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Official: N. Korea may be planning missile test

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Official: N. Korea may be planning missile test03:42

"We've identified that malicious codes had spread to some computers in the intranet system," he said.

"The Ministry of National Defense assembled a joint investigation team, and after the investigation, we've confirmed that some military data, including confidential information, was leaked. North Korea is assumed to be behind this," Moon told reporters.

The South Korean military still has not determined what exactly has been leaked, Yonhap News reported, but said it was possible the hack could lead the command to rewrite military operation plans.

If the accusations are true, it wouldn't be North Korea's first breach of South Korea's cybersecurity this year.

In March, top South Korean government officials' smartphones were hacked by North Korea, according to the country's spy agency, stealing text messages and voice communications by "sending enticing text messages."